Spare parts

In 1859, after Charles Darwin mooted his monstrous, marvellous idea, people quickly set to work misunderstanding it. Victorian naturalists had hitherto accepted that the objects of their fascination were the flawless creations of a perfect God. Even today, we tend to misconstrue evolution as the inexorable pursuit of perfection.

Well, it’s not. Nothing’s perfect. Least of all, you and I. Evolution creeps along courtesy of mutations—mistakes in the replication that happens when reproductive cells divide. These glitches are random, which means some can turn out to be a good thing, others not so much.

Darwin assured us that natural selection would soon see off any handicaps.

“We may feel sure that any variation in the least degree injurious would be rigidly destroyed,” he wrote in On the Origin of Species. He was right—sort of. The rigours of competition might eventually weed out compromised or maladapted individuals, but environmental change often happens way faster, leaving evolution struggling to keep up.

Our DNA is in catchup. We still possess features and behaviours wrongfooted by contingency, brokered millions of years ago when the world bore almost no resemblance to this one.

Some are, at best, an anachronism, at worst, a pain in the arse. We used to need appendixes and little toes—now we don’t, but evolution doesn’t know that yet.

Ever since the end of the ice ages, animals, including humans, have been getting smaller. That’s why there’s no longer enough room in your jaw for your third molars—your wisdom teeth—and because we no longer have to grind away on raw food, our other molars don’t wear down so fast, which only makes the overcrowding worse—but your DNA prescribed them anyway.

In 1893, German anatomist Robert Wiedersheim made a list of 86 ‘vestiges’, parts of the human body that appeared to be of little use. These were leftovers of the evolutionary process, he determined. The word ‘vestige’ is derived from the Latin word for ‘footprint’—these structures are traces of our ancestors, clues to our history, and points of connection to other mammals. At worst, this evolutionary baggage is damaging to human health—ask anyone who’s had their wisdom teeth, tonsils or appendix removed. At best, these features are useless.

But it looks as though evolution may finally have tumbled to our plight: nowadays, around 35 per cent of people never develop wisdom teeth at all, a portent that dentistry may not be so lucrative in the 22nd century.

Similarly, you may be the owner of a VNO—a vomeronasal organ—or you may not. All reptiles, amphibians and many mammals use theirs to detect chemical cues and, in some cases, communicate with others through the medium of pheromones. But so atrophied is the human VNO that researchers can’t even agree on whether we all have one. Even if you do, it has been disconnected—searches have failed to find any of the associated sensory neurons and axions that pack the noses of other animals. So those pheronome sprays have no way of landing you a date.

Adaptations aren’t all physical. Our DNA also ordains our reflexes, and it turns out we’re still slaves to a few obsolete impulses. As if hiccups aren’t irritating enough, we get them for no good reason. Our amphibious ancestors used them to close the glottis before forcing a mouthful of water out through their gills. Lungfish and tadpoles still do—a reflex mediated by neurons in their brainstem. Your own brainstem still has that architecture, so archaic that it evolved even before consciousness, which is why you can’t use your mind to quell hiccups.

Seems we’re stuck with some redundant reflexes—others, we’re turning to new uses. When my Labrador is feeling unsure or intimidated, his hackles go up: the hairs along his neck and back stand erect, making him look bigger and more alpha, concealing his true, wussy self.

Lots of animals use this pilomotor reflex to clench the tiny muscles at the base of each follicle, pulling fur, feathers or spines upright to look big and boss, or to trap warm air close to the skin when it gets cold. You do it, too, when you’re frightened, or angry—we call it getting the goosebumps—even though your feeble fur is no longer thick enough either to warm you up or puff you up.

But goosebumps may have a new function. I can’t listen to Beethoven’s ‘Ode to Joy’ without getting a tingling frisson of them. Evolutionary biologists think goosebumps may amplify our emotional responses, exciting receptors in the brain’s reward centre. (Flushing is another thermoregulatory mechanism that also doubles as a reward signal.)

Sometimes, the mishaps of evolution work in reverse: we’ve dumped some adaptations that would come in really handy today. Doctors tell us we need a range of vitamins to function, but none so important as vitamin C (the recommended daily intake, 60 milligrams, is the highest of any vitamin required by humans). Unlike most other creatures, we can’t make our own. We used to, millions of years ago, and we still possess the gene that codes for gulonolactone oxidase, the enzyme that produces vitamin C, but a series of mutations have shut it down.

Why? Because, as omnivores, we could always get enough vitamin C from our diet. As long as that diet didn’t change, there was no evolutionary penalty for halting in-house production. Scant comfort to sailors stricken by scurvy.

It would seem evolution eventually heeds signals, environmental and experiential. Sometimes, though, it’s painfully slow to take a hint.

Gentlemen, ponder your testicles. Why did evolution tack them onto us that way—an overt, unpadded afterthought to be struck, sat on and sunburnt?

Of all the agonies known to man, there is nothing quite like the seismic trauma of a blow to the testicles. Furthermore, a quarter of men will suffer a groin hernia—where an organ pops out of the tissue that holds it in place—thanks to a weak spot in their abdominal wall where their testicles exited during puberty. Sure, it’s easily fixed nowadays, but we’ve had surgeons and sutures for only a tiny fraction of our existence. For millions of years, groin hernias have been killing their owners.

So, if fortune favours the well adapted, why do men still have to make subtle adjustments before they can sit down? You’ve probably remembered the answer: that our testes prefer a temperature slightly lower—two degrees Celsius less—than our other organs. Sperm cells like it not so hot, which is why testicles move during our infancy to outside the abdominal cavity.

But why? Ovaries cope inside just fine. So does bone marrow, which churns out blood cells. Evolution might just as easily have tweaked testes to work at the same temperature as the rest of us. But it hasn’t—yet. The simple fact is that there’s no good reason for dangly bits—only that Nature’s always done it that way.

Perhaps we can take solace from the fact that nobody’s perfect. You don’t need to be flawless to survive—just better built than the competition.